SAN DIEGO, CA—Low-dose naltrexone may be an effective, highly tolerable, and inexpensive treatment for patients with fibromyalgia, according to results of a prospective, open-label study presented at the 2013 ACR/ARHP Annual Meeting.

Fibromyalgia has been classified as a “central sensitivity syndrome” mediated by centrally acting proinflammatory cytokine activity, which can cause symptoms of fibromyalgia.

Noting that a significant number of patients with fibromyalgia do not respond adequately to currently available therapies, Samy Metyas, MD, assistant clinical professor of medicine at University of Southern California, Los Angeles, CA, and colleagues administered naltrexone 3mg at nighttime to 25 patients—24 females and 1 male—diagnosed with fibromyalgia based on American College of Rheumatology criteria. The dose could be titrated to a maximum of 4.5mg. Patients were permitted to continue pregabalin, milnacipran, or duloxetine.

Of the 22 patients completing the study, 7 (32%) remained on naltrexone monotherapy throughout the study. At Month 3, a 19.5% overall improvement in FIQR was reported. Eleven patients (50%) had an average of a 41% improvement in FIQR.

Naltrexone is an opioid receptor antagonist used to treat alcohol and opioid dependence. They hypothesized that low-dose naltrexone—an opioid-receptor antagonist used to treat alcohol and opioid dependence—“causes transient blockade of opioid receptors centrally, resulting in a rebound of endorphin function which may attenuate pain in fibromyalgia.”

Further randomized controlled trials and larger studies are needed to further assess the efficacy of naltrexone in fibromyalgia, the investigators concluded.

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